Treating sulphite pulp



Patented July 31, I934 TREATING SULPHITE PULP Harold R. Murdock, Canton, N. 0., assignor to The Champion Fibre Company, Canton, N. 'C., a

corporation of Ohio No Drawing. Application April 3, 1933,

Serial No. 664,287

7 Claims.

This invention relates to the art of preparing pulp for paper manufacture and is concerned with the production and utilization of a sulphite pulp from coniferous pine wood.

When coniferous pine woods are digested with those reagents commonly employed in the sulphite or acid process, it is found that even when young-or small diameter wood is used the pulp obtained is specked with globules of resin of about the same size as the resin present in the wood, and also that the pulp contains a relatively large amount of shives or fiber bundles from which the cellulose fibers have not been completely liberated. The chiefreason for the large amount of resin and shives present in the pulp is that the so-called sulphite cooking liquors are of necessity acid in character, and, primarily because of this,

-- the resin is not dissolved. Because these resins are more readily dissolved by alkaline reagents, it has become common commercial practice to pulp coniferous pine Woods by an alkaline process such as the soda process or the sulphate process. Pulps produced by such alkaline processes are more nearly free from resin and shives than pulps produced by the sulphite process, but are not as white in color as the pulp produced by the sulphite process, and for that reason do not lend themselves inthe unbleached condition to the manufacture of certain types of paper, such as newsprint, tag sheets, manila wrappers, etc., as do the sulphite pulps.

The presence of these globules of resin in the sulphite pulp obtained from coniferous pine woods, however, makes it extremely difficult to use this pulp in commercial practice of fabricating paper from the pulp because the resin clings to the screens, paper machine wires and rolls, eventually necessitating the stopping of production until the accumulated resins have been removed from the equipment. Experience has shown, however, that this resin would not produce this particular trouble if it-were dispersed in the pulp, such as is done when paper is sized. It seems to be the physical condition of the resin present rather than-the presence of the resin, which gives the aforementioned difiiculty in operation.

In pulping coniferous pine wood by the sulphite process, not only is the heartwood difilcult to pulp, but the relatively harder and denser summer wood of the sapwood portion of even young trees is quite refractory in the pulping operation, and, along with the heartwood, is recovered in large amounts as screenings, that is, those portions of the wood which have faile to liberate the cellulose fibers sufllciently sot ey can pass through the slotted screens. when a pulping operation yields a relatively high percentage of such screenings, the screened pulp invariably contains in substantial amounts shives ononly partially liberated fiber bundles, whicmfliowever, are of sufflciently small size to have passed through the slotted screens. These so-called shives are very undesirable as they clearly appear in the finished sheet of paper, giving such paper a dirty, low

. quality appearance.

An object of this invention is the provision of a mode of processing the pulp obtained by digesting coniferous pine wood by the usual sulphite process, in order to disperse the globular resinous matter throughout the pulp in a uniform manner and simultaneously disintegrate the fiber bundles so that the cellulose fibers are substan-. tially liberated.

My process consists essentially in treating an aqueous suspension of pine sulphite pulp, prepared in any well known manner, with an alkaline reagent for a sufficient period of time, in an amount sufiicient to dissolve and/or disperse the resin contained in said pulp, and then adding to the so treated pulp the other pulps and other ingredients necessary for making the furnish including a precipitant for the dissolved or dispersed resin, and then beating, hydrating or working the resulting stuii in the usual and well known manner for preparing and forming a sheet of paper. I find that by treating the resinous pine pulp in this manner the resin contained therein is converted into a soluble soap, which latter is retained in the pulp suspension, in lieu of added size, and is precipitated in a-uniform condition in and over the fibers by the subsequent addition of alum or its equivalent, whereby the resulting paper sheet is made free from resin specks and at the same time is sized. It, of course,

does not involve a departure from this concept to add additional size to the stock if the amount of size created in the stock by the carrying out of the above-described operation is deemed insuflicient for the particular result desired. A second result of this treatment is the softening of the shives so that the fibers thereof are liberated, the pulp made more uniform, and the resulting paper made more nearly free from shives.

The invention will be described more particularly by reference to the following illustrative example:

Young, green jack pinewas chipped and charged to the digester bin. Approximately 46,500 pounds of this was charged to the digester and 37,500 gallons of sulphite cooking liquor introduced. The cooking liquor analyzed 5.47% total S02, 3.97% free S02 and 1.50% S02 combined with lime. Duringa period of six hours the temperature was gradually increased to 300 F.', and for a period of seven more hours this latter temperature was maintained. The digester was relieved of exthe digester was blown to a large blow pit and the pulp drained free of cooking liquor. The pulp was washed by displacement until the wash water was clear. The pulp was then screened and the total amount of screenings and knots found to be about 8% of the wood charged. The resultant pulp showed, on analysis, a resin content of 1.12% and a considerable amount of shives were present, which made a test paper sheet, laid up therefrom, appear decidedly dirty.

One thousand pounds of the pulp, coming from the screen room, was charged to a beater of the usual type in which the furnish for the paper is prepared. To this unbleached pulp in the beater was added ten pounds of caustic soda and the pulp was beaten in the resulting alkaline liquor for thirty minutes. Thereby the resin content of the pulp (both that occurring therein in the form of globules and that contained in the shives) was dissolved in the form of resin size. To the resulting suspension of beaten pulp in aqueous alkaline size-containing liquid there were then added the following furnish ingredients in the amounts stated:

Soda pulp 300 pounds Acid blue .70 ounce Alum 30 pounds and the resulting stock mixture was agitated until the ingredients were thoroughly mixed and then was passed through a Jordan engine and thence to the paper machine. It was found that the so-produced stock did not gum the wire of the stock screens or of the Fourdrinier machine, that the solubilized resin had been precipitated in the form of aluminum resinate uniformly over the fibers, and that the resulting paper sheet was sized; moreover, that the resulting paper sheet showed no resin specks and practically no shives.

It will, of course, be appreciated that the abovedescribed specific cooking or digesting schedule may be modified without departing from the scope of the present invention, the crux of the present invention residing mainly in the above-described concept of converting the resin content of a resinous pulp into a useful furnish constituent, simultaneously liberating fibers from fiber bundles contained in the pulp, and utilizing the said furnish constituent in said pulp in the making of paper therefrom.

For instance, itmight be found desirable to disperse the resin in the pulp and precipitate it onto the fibers before screening the pulp, although, obviously, it would be more advantageous in most instances to perform the step on the screened pulp in the beater. Then, again, it might be desirable for, some purposes to precipitate the resin onto the fibers before adding the other furnishing ingredients to the pulp. These and other such modifications should be considered within the scope of this invention.

In place of caustic soda, it will also be appreciated that other solvents of resin can be used, such as soda ash, sodium silicate, trisodium phosphate, etc., without departing from the spirit of this invention.

It should be apparent, also, to those familiar with this art that it is within the scope of this invention to bleach the untreated pine pulp before dispersing the resin with an alkaline reagent, as is herein specified; also that for some particular reason it might be desirable to bleach the pulp after the treatment with an alkaline reagent but before converting the'pulp into the paper product.

I claim:

1. Process which comprises treating a resinous sulphite pulp from resinous coniferous wood, in aqueous suspension, with an alkaline reagent in an amount suflicient at least to disperse the resin contained in said pulp, with agitation, and thereafter precipitating the so-dispersed resin over the pulp fibers by adding to the resulting mixture a resin-precipitating agent.

2. Process which comprises treating a resinous sulphite pulp from resinous coniferous wood, in aqueous suspension, with an alkaline reagent in an amount suflicient to disperse and solubilize the resin contained in said pulp, agitating the pulp and alkaline reagent, and thereafter precipitating the so-dispersed and solubilized resin over the pulp fibers by adding to the resulting mixture a resin-precipitating agent.

3. Process which comprises treating a resinous sulphite pulp from resinous coniferous wood, in aqueous suspension, and after screening but before addition thereto of furnish ingredients, with an alkaline reagent in an amount sufficient at least to disperse the resin contained in said pulp, with agitation, and thereafter precipitating the so-dispersed resin over the pulp fibers by adding to the resulting mixture a resin-precipitating agent. 108

4. Process which comprises treating a resinous sulphite pulp from resinous coniferous wood, in aqueous suspension, and after screening but before addition thereto of furnish ingredients, with an alkaline reagent in an amount suihcient to 110 disperse and solubilize the resin contained in said pulp, agitating the pulp and alkaline reagent, -and thereafter precipitating the so-dispersed and solubilized resin over the pulp fibers by adding to the resulting mixture a resin-precipitating agent.

5. Process which comprises treating a resincontaining sulphite pulp from resinous coniferous wood, in aqueous suspension, and after screening but before addition thereto of furnish iiigredients, with an alkaline reagent in an amount suflicient to disperse and solubilize the resin contained in said pulp, and thereafter adding to the resulting mixture furnish ingredients including a precipitant for solubilized resin.

6. Process which comprises treating a resincontaining sulphite pulp'from resinous coniferous wood, in aqueous suspension, and after screening but before addition thereto of furnish ingredients, with an alkaline reagent in an amount .130 sufficient to disperse and solubilize the resin contained in said pulp, and thereafter adding to the resulting mixture furnish ingredients including a precipitant for solubilized resin and forming the so-prepared furnish into paper.

7. Process which comprises digesting resinous coniferous wood chips in acid sulphite cooking liquor under conditions of elevated temperature and elevated pressure, draining and washing the resulting sulphite pulp, screening the washed 1 9 sulphite pulp in aqueous suspension, adding to the screened suspension of sulphite pulp a relatively small but eflective amount of caustic alkali and agitating the resulting mixture, adding to the agitated mixture furnish a precipitant for solubilized resin, and forming the product into paper.

HAROLD R. MURDOCK.

ents including J45 

